There is a considerable amount of prior art regarding the immobilization of E. coli or other microbial cells for use in the preparation of L-aspartic acid. For example, U.S. Pat. No. 3,791,926 (Chibata et al) describes a process for the production of L-aspartic acid which involves polymerizing a monomer selected from acrylamide, N,N'-lower alkylene-bis(acrylamide) and bis(acrylamidomethyl)ether in an aqueous suspension containing an aspartase-producing microorganism such as E. coli ATCC No. 11303. The resultant immobilized aspartase-producing microorganism is treated with ammonium fumarate or a mixture of fumaric acid or its salt and an inorganic ammonium salt which by enzymatic reaction gives L-aspartic acid.
The immobilization of E. coli cells containing aspartase activity and use of the resulting immobilized cells for the production of L-aspartic acid are also described by Fusee et al, Applied and Environmental Microbiology, Vol. 42, No. 4, October 1981, pages 672-676. According to Fusee et al, the cells are immobilized by mixing a suspension of the cells with a liquid isocyanate-capped polyurethane prepolymer (Hypol.RTM.) so as to form a "foam" containing the immobilized cells.
Sato et al (Biochimica et Biophysica Acta, 570 (1979) pages 179-186) have disclosed the immobilization of E. coli cells containing aspartase activity with .kappa.-carrageenan, and use of the immobilized preparation for the production of L-aspartic acid.
Additional literature disclosures describing the immobilization of microbial cells in urethane prepolymers or polyurethanes or the like include the following:
(a) Immobilization of Microbial Cells in Polyurethane Matrices by Klein et al, Biotechnology Letters, Vol. 3, No. 2, 65-70 (1981);
(b) Hydrophilic Urethane Prepolymers: Convenient Materials for Enzyme Entrapment, Biotechnology & Bioengineering, Vol. XX, pages 1465-1469 (1978);
(c) Transformation of Steroids by Gel-Entrapped Cells in Organic Solvent by Omata et al, European J. Applied Microbiology and Biotechnology 8, 143-155 (1979); and
(d) Entrapment of Microbial Cells and Organelles With Hydrophilic Urethane Prepolymers, by Tanaka et al, European J. Applied Microbiology and Biotechnology, 7, 351-354 (1979).
The above-noted processes for preparing L-aspartic acid using immobilized microbial cells suffer from various disadvantages. For example, .kappa.-carrageenan gum and polyurethane "foam" as disclosed by Fusee et al and Sato et al are relatively soft and compressible. Hence when these immobilized cell compositions are used, in a column through which ammonium fumarate is passed for conversion to ammonium aspartase, they tend to be compressed and plug up, particularly where high flow rates and/or relatively tall column heights are involved.